T-Mobile has backtracked on its decision to drastically cut the mobile data use allowances for existing as well as new smartphone customers, following an explosion of public anger at the move.

On Thursday, the operator said it will now only offer the reduced levels of data to new and upgrading customers, while existing customers will get the 1-3GB they signed up for until their contracts run out.

The U-turn, announced on Thursday afternoon, came shortly after the consumer group Which? said its legal team were of the opinion that T-Mobile was breaking its own terms and conditions by announcing the 'fair use' cap cut less than a month after it will come into force on 1 February. The cut, which will mean an 83 percent reduction in the amount of data an Android user is supposed to use each month--from 3GB to 500MB--was only announced over the weekend.